Allow only specific values for key in Joi schema

If you want to accept one or more values (apple, banana or both) you can use allow: https://joi.dev/api/?v=17.3.0#anyallowvalues

You can also use valid like

const schema = joi.object().keys({
  query: joi.object().keys({
    // allow only apple and banana
    id: joi.string().valid('apple','banana').required(),
  }).required(),
})

Reference: https://github.com/hapijs/joi/blob/v13.1.2/API.md#anyvalidvalue---aliases-only-equal

You can try with .valid() to allow joi only with that specific string .

const schema = joi.object().keys({
  query: joi.object().keys({
    role: joi.string().valid('admin','student').required(), // joi would allow only if role is admin or student.
  }).required(),
})

This is absolutely equal to giving "enam" field in mongoose ODM for representing objects in mongodb.